Visit the British Museum if you can. See all our imperial plunder. And the mummies. Everyone loves the mummies.
Whenever I've been to a museum containing mummies, there has always been at least one person pointing at the mummies, laughing. I have learnt from this experience that many people find the shape of an antique, mummified crotch hilarious.
Haha, in all honesty though, where you want to go depends on what you want to do. It has been said that the Lake District has some of the most beautiful scenery on the planet by this man. Whilst it also has huge manour houses filled with history and some of the greatest cathedrals ever built, even though every Spanish cathedral rivals the best of the English imo.
Talking about cathedrals, go to Gloucestershire cathedral, where some of the harry potter filming was done, it is a amazing place. My opinion anyway.